What catches me with a comic is...
Good art first off, if their technical skill is at a certain level of unplished, it's hard to get into the story. Having a good style is very important to me personally, and I don't just mean "draws like god blessed their fingertips". I mean is it unique? Does it have appeal? Is the basic stuff like anatomy and lineart solid? If so, usually I'll give it a shot.
Then it's writing. So many comics have lost me because their dialogue sounds dry and lifeless, or because I can tell they didn't do their research on something I personally care about. Or because there just isn't a REASON to keep reading.
Questions. Make me ask questions. Not yes or no questions. "Who is Gretta?" questions "What was THAT??" questions. Then slowly build me up to the answer over time. Once that question is done, propose a new one. It's irresistible. I guarantee you I will swipe right to see more pages until I can no longer.
Last is well....relationships. Not just shipping (though that's a bonus) but like, make me CARE about these characters and their relations with one another. Make the reader want to explore relations between your characters. Especially romantic ones, cause people LOVE to ship things.
If a story has all this usually it ends up on my "DUDE have you read x????" list.